Direct current polarity control circuit



a 3,267,301 P tented August 16, 1966 3,267,301 DIRECT CURRENT POLARITYCONTROL CIRCUIT Roy G. Gignac, Roselle, Ill., assignor to ElectronicComponents Corporation, Addison, 111., a corporation of Illinois FiledDec. 16, 1963, Ser. No. 330,892 2 Claims. (Cl. 307-127) This inventionrelates to a circuit for ensuring a consistent polarity across a pair ofload terminals for random positioning of a D.C. voltage source across apair of direct current input terminals.

Direct current polarity control circuits performing the function abovedescribed are well known in the art. They generally include a relay anda rectifier in series across :a pair of direct current input terminals,the rectifier effecting energization of the relay for a first relativepolarity across the input terminals and eilecting the de-energization ofthe relay for the opposite relative polarity across said inputterminals. The relay is generally provided with double pole, doublethrow contacts which nor.- mally ensure the proper polarity across theload terminals for the energized and de-energized conditions of therelay respectively, since these conditions of the relay are normallytied in directly with the polarity of the voltage applied to the inputterminals. However, this circuit suffers from one important disadvantagewhich is that failure of the relay to operate in the normal manner dueto an open circuit in the relay coil or the like can cause -a voltage ofimproper polarity to appear across the load terminals, which couldseriously damage the load connected to these terminals.

The present invention overcomes this disadvantage by ensuring a properpolarity across the load terminal when the relay is in proper operatingcondition, and the com plete disconnection of the input voltage from theload terminals in case the relay is not operating. In such case, theload is protected against the presence of a voltage condition across theload terminals which is of an improper relative polarity.

Another important advantage of the invention is that it not only has thefunctional advantage referred to, but it also results in a substantialreduction in cost of the circuit involved. For example, a cost reductionas much as fifteen percent (15%) can be achieved by utilizing thecircuit of the present invention in low current circuits.

The accompanying drawing is a circuit diagram i1lustrating one exampleof the invention.

An exemplary direct current polarity control circuit of the presentinvention is identified in the drawing by reference numeral 2. Thecircuit is arranged to form an integral unit with an input plugconnector 4 insertable into a suitable wall or other outlet socket 5having socket terminals 5a and 5b connected to a suitable source ofdirect current voltage. The socket terminal 5a is permanently connectedto the positive terminal of the voltage source and the socket terminal5b is permanently connected to the negative terminal. The plug connector4 has plug terminals 4a and 4b which constitute input terminals to thecircuit 2. The circuit 2 has load terminals 6a and 6b across which inputterminals 8a and 8b of a suitable load device 8 is connected. It isassumed that the load device is one wherein the input terminal 8a mustbe positive with respect to the input terminal 8b either to ensureproper operation of the load device 8 or to protect the same from damageand that the plug connector 4 can be inserted into the socket 5 ineither one of two positions so that plug connector terminal 4a may beeither positive or negative with respect to the plug connector terminal4b. The direct current polarity control circuit 2 ensures that the loadterminal 6a is positive with respect to the load terminal 6bindependently of whether plug connector terminal 4a is in contact withsocket terminal 5a or 5b.

A bus L1 is connected to plug connector terminal 4a through an on-ofiswitch 13 and a bus L2 in connected to the plug connector terminal 4b. Aseries circuit including a rectifier 12 and the coil of a relay R1 areconnected in series between the busses L1 and L2. The anode 12a of therectifier 12 is connected to the upper end of the relay coil and thecathode 12b of the rectifier 12 is connected to the bus L1. Thus,whenever the bus L1 is positive with respect to the bus L2, therectifier 12 will block the flow of direct current to the relay coil sothat the relay R1 will-remain in a de-energized state. When the bus L1is negative with respect to the bus L2, the rectifier 12 will conductdirect current to the relay coil to energize the same.

Relay R1 has a movable contact R1-1 which, in the de-energized state ofthe relay, contacts a stationary contact R1-2 connected by a conductor15 to the bus L1. In the energized state of the relay R1, the movablecontact R1-1 is connected to a stationary contact R1-3 connected by aconductor 17 to the bus L2.

The circuit of the invention is completed by a pair of rectifiers 19 and21. The cathode 21a of the rectifier 21 is connected to the bus L2 andthe anode 21b thereof is connected to the load terminals 6b. Thus, whenthe relay R1 is de-energized due to the fact that the bus L1 is positivewith respect to the bus L2, the path of current flow between the bussesincludes stationary contact R1-2 connected to bus L1, movable contactR1- 1, load terminal 6a, the load device 8, load terminal 6b andrectifier 21 connected to bus 12. In such case, the load terminal 611 ispositive with respect to load terminal 6b.

The cathode 19a of rectifier 19 is connected to the bus L1 and the anode1% thereof is connected to the load terminal 6b. When the bus L1 ispositive with respect to the bus L2, which is the condition when therelay R1 is de-energized, the rectifier 19 is in a non-conductive statebecause the cathode 19a thereof is positive with re spect to its anode19b.

When the bus 11 is negative with respect to the bus L2, so that therectifier 12 will conduct current to energize the relay R1, movablecontacts R11 will separate from the stationary contact R1-2 and makecontact with the stationary contact R1-3. Then, the path of current flowbetween the busses L1 and L2 can be traced through the conductiverectifier 19 connected to the bus L1, load terminal 6b, load device 8,load terminal 6a, movable contact R1-1 and stationary contact R1-3connected to bus L2. In this case also, the load terminal 6a is positivewith respect to the load terminal 6b. When the bus L1 is negative withrespect to the bus L2, the rectifier 21 is in a non-conductive statebecause its cathode 21a is then positive with respect to its anode 21b.

One of the main advantages of the invention, as above indicated, is thereliability of the circuit in the event the relay R1 should fail tooperate. Thus, if the coil of the relay R1 were to be open circuited,since the relay R1 cannot be energized when the bus L1 is negative withrespect to the bus L2, movable contact R1-1 of the relay Rl remains incontact with its stationary contact R1-2 but then will not result in thefeeding of the positive voltage on the plug connector terminal 4b to theload terminal 6b which could damage the load device -8 because therectifier 21, as above indicated, will then be in a nonconductive statebecause the cathode 21a is positive with respect to the anode 21b andthere is no other path for this positive voltage to reach load terminal6b. Similarly, if for some reason movable contact R1-1 should be comestuck to the stationary contact R1-3 when the relay 'R1 is energized,the subsequent de-energization of the relay will not result in a voltageof improper polarity on the load terminals because the rectifier 19 willblock conti-nuity between load terminal 6b and the then positive bus L1.

As above indicated, in' addition to the functional'advantage of thecircuit just explained, utilization of the rectifiers 19 and 21 resultsin a substantial reduction in the cost of the circuit in comparison to acircuit of the type heretofore utilized where the relay R1 was providedwith two sets of movable and stationary contacts.

I claim:

1. A direct current polarity control circuit connected between a firstand a second direct current input terminal across which a direct currentvoltage source is to be connected in a random fashion, so that the inputterminals may have either one of two relative polarities, and a firstand a second load terminal across which a direct current voltage is tobe applied having a consistent relative polarity, said circuitcomprising: a relay and a first rectifier connected in series acrosssaid input terminals for effooting the energizing for said relay whensaid input terminals have a first relative polarity and thede-energizing of said relay when said terminals have the oppositepolarity, said relay having a movable contact connected to said firstload terminal and a first and a second stationary contact respectivelyconnected to said first and second input terminals, said movable contactbeing connected to said first stationary contact when said relay isde-energized and to said second stationary contact when said relay isenergized, a second rectifier connected between said second loadterminal and said second input terminal for coupling the direct currentinput voltage to said load terminals when the relay is de-energized, andfor decoupli-ng the input voltage from the load terminals when saidinput terminals have said first relative polarity, and a third rectifierconnected between said second load terminal and said first inputterminal for coupling the voltage of said input terminals to said loadterminals when said relay is energized and for decoupling the inputvoltage from said load terminals when the voltage across said inputterminals has said opposite polarity.

2. A direct current polarity control circuit having a connector with afirst and a second input terminal which can be randomly removablyconnected in either of two ways to a mating connector coupled to asource of dir ect current voltage, so that said input terminals may haveeither one of two relative polarities, and a first and a second loadterminal across which a direct current voltage is to be applied having aconsistent relative polarity, said circuit comprising: a relay and afirst rectifier connected in series across said input terminals foreffecting the energizing for said relay when said input terminals have afirst relative polarity and the de-energizing of said relay when saidterminals have the opposite polarity, said relay having a movablecontact connected to said first load terminal and a first and a secondstationary contact respectively connected to said first and second inputterminals, said movable contact being connected to said first stationarycontact when said relay is de-energized and to said second stationarycontact whenv said relay is energized, a second rectifier connectedbetween said second load terminal and said second input terminal forcoupling the direct current input voltage to said load terminals whenthe relay is de-energized, for decoupling the input voltage from theload terminals from said load terminals when said input terminals havesaid first relative polarity, and a third rectifier connected betweensaid second load terminal and said first input terminal for coupling thevoltage of said input terminals to said load terminals when said relayis energized and for decoupling the input voltage from said loadterminals when the voltage across said input terminals has said oppositepolarity.

No references cited.

ORIS L. RADER, Primary Examiner. W. SHOOP, Assistant Examiner.

1. A DIRECT CURRENT POLARITY CONTROL CIRCUIT CONNECTED BETWEEN A FIRSTAND A SECOND DIRECT CURRENT INPUT TERMINAL ACROSS WHICH A DIRECT CURRENTVOLTAGE SOURCE IS TO BE CONNECTED IN A RANDOM FASHION, SO THAT THE INPUTTERMINALS MAY BE EITHER ONE OF TWO RELATIVE POLARITIES, AND A FIRST ANDA SECOND LOAD TERMINAL ACROSS WHICH A DIRECT CURRENT VOLTAGE IS TO BEAPPLIED HAVING A CONSISTENT RELATIVE POLARITY, SAID CIRCUIT COMPRISING:A RELAY AND A FIRST RECTIFIER CONNECTED IN SERIES ACROSS SAID INPUTTERMINALS FOR EFFECTING THE ENERGIZING FOR SAID RELAY WHEN SAID INPUTTERMINALS HAVE A FIRST RELATIVE POLARITY AND THE DE-ENERGIZING OF SAIDRELAY WHEN SAID TERMINALS HAVE THE OPPOSITE POLARITY, SAID RELAY HAVINGA MOVABLE CONTACT CONNECTED TO SAID FIRST LOAD TERMINAL AND A FIRST ANDSECOND STATIONARY CONTACT RESPECTIVELY CONNECTED TO SAID FIRST ANDSECOND INPUT TERMINALS, SAID MOVABLE CONTACT BEING CONNECTED TO SAIDFIRST STATIONARY CONTACT WHEN SAID RELAY IS DE-ENERGIZED AND TO SAIDSECOND STATIONARY CONTACT WHEN SAID RELAY IS ENERGIZED, A SECONDRECTIFIER CONNECTED BETWEEN SAID SECOND LOAD TERMINAL AND SAID SECONDINPUT TERMINAL FOR COUPLING THE DIRECT CURRENT INPUT VOLTAGE TO SAIDLOAD TERMINALS WHEN THE RELAY IS DE-ENERGIZED, AND FOR DECOUPLING THEINPUT VOLTAGE FROM THE LOAD TERMINALS WHEN SAID INPUT TERMINALS HAVESAID FIRST RELATIVE POLARITY, AND A THIRD RECTIFIER CONNECTED BETWEENSAID SECOND LOAD TERMINAL AND SAID FIRST INPUT TERMINAL FOR COUPLING THEVOLTAGE OF SAID INPUT TERMINALS TO SAID LOAD TERMINALS WHEN SAID RELAYIS ENERGIZIED AND FOR DECOUPLING THE INPUT VOLTAGE FROM SAID LOADTERMINALS WHEN THE VOLTAGE ACROSS SAID INPUT TERMINALS HAS SAID OPPOSITEPOLARITY.